The Animal Core provides the investigators with chronically instrumented sheep and with non instrumented pregnant and nonpregnant animals. The specific goals of the Animal Core are: to obtain time- dated pregnant animals at 75 days of gestation; to prepare chronically instrumented juvenile and adult sheep for use in the different research projects; to conduct necropsies and facilitate the collection of tissues; and to facilitate the in vivo studies involving monitoring physiologic variables under acute or chronic conditions. Pregnant ewes are randomly assigned to receive either vehicle or betamethasone injections at 80 an 81 days gestation and lambs are allowed to deliver spontaneously at term. The Animal Core is essential for three of the research projects. The director of the core has more than 25 years of experience working with chronically instrumented fetal and pregnant animals. The Core provides the unique combination of the ability to infuse physiological amounts of putative regulators, the availability of plasma samples, in vivo recording of physiological variables and tissues for in vitro studies from the same animal in which in vivo studies have been conducted. Sheep will be chronically instrumented in order to obtain physiological data in animals that are not under the stress of anesthesia. We will use fime dated pregnant sheep provided to us by Hash, Inc. The supplies maintains a very large flock and has consistently provided us with healthy and accurately dated pregnant animals. All of these surgeries and manipulafions will be conducted within the Animal Core in the Perinatal Research Laboratory. Pregnant and adult sheep of both genders will be used. Betamethasone is administered in a manner similar to that used for stimulafing lung maturafion in the unborn human, i.e., two doses of a mixture of the acetate and phosphate form, given 24 hours apart. The only difference is that we will adjust for maternal body weight and give 0.17 mg/kg with a maximum of 12 mg/day.